Harnessing the many favorable properties of ionic liquids in a solid electrolyte thin film form is desirable for a host of electrical energy storage applications, including electrochemical double layer capacitors. Using a cross-linked polymer matrix to provide structural support, freestanding ionogel materials can be achieved with a wide range of polymer weight fractions. Compression testing and impedance spectroscopy have been used to characterize the mechanical and electrical responses of ionogels containing between 4.9 and 44.7 wt % poly(ethylene glycol) diacrylate. Although the elastic modulus of these solid electrolyte materials is observed to vary by more than 4 orders of magnitude within the composition range studied, concomitant changes in gel ionic conductivity and double layer capacitance were much less dramatic.

Three room-temperature ionic liquids (ILs), differing only in anion identity [1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (EMI FAP), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI TFSI), and 1-ethyl-3methylimidazolium tetracyanoborate (EMI TCB)], are employed to directly compare the mechanical and electrical responses of cross-linked, poly(ethylene glycol) diacrylate (PEGDA)-supported ionogel solid electrolytes. It is observed that the choice of IL influences the minimum amount of polymer required to create a non-flowing gel, but not the value of the Young's modulus for a given weight fraction of PEGDA above the gelation point. Furthermore, the relative decrease in ionic conductivity above the gel point is also found to be IL-independent. These observations suggest that IL contributions to the character of these ionogels can be distinguished from the contributions of the supporting polymer scaffold. In addition, an extremely large ionic conductivity value (13.1 mS cm À1 ) is achieved at room temperature using EMI TCB at its gelation point (7.2 wt % PEGDA).Ionogels are a class of composite solid electrolyte materials consisting of an ionic liquid (IL, room-temperature molten salt) that is supported by a solid scaffold. They have recently been explored for numerous electrochemical device applications, including batteries, [1][2][3] dye-sensitized solar cells, [4] electrochemical capacitors, [1,[3][4][5][6][7][8][9][10][11][12][13] and sensors. [1] The use of ILs in gel form is a rapidly growing field of research, which has expanded over the past decade because of the many beneficial properties of ILs for electronic applications, such as negligible volatility, low flammability, wide electrochemical window, ionic conductivity, and tunable solubility. [1,14] Ionogels have been created by using a variety of approaches; typical routes include mixing a solid support (e.g. a triblock copolymer) [6,12,15] into an IL (often using a co-solvent), in situ radical polymerization of a monomer inside an IL, [5,10,16,17] formation of a solid scaffold in situ through sol-gel reactions, [1,18] and various combinations of these methods. [8,13,19] The discovery of new ILs has grown rapidly in recent years; however, one of the most highly studied classes encompasses ILs based on the N,N'-dialkylimidazolium cation. [1,3,20] For the 1ethyl-3-methylimidazolium (EMI) cation in particular, many investigations have focused on its pairing with the bis(trifluoromethanesulfonyl)imide (TFSI) anion, which together yield a hydrophobic IL with a relatively high ionic conductivity and a wide electrochemical window. [20] In addition to the TFSI anion, two other EMI-based ILs have recently emerged as promising candidates for electrochemical device applications. EMI tetracyanoborate (TCB) has garnered interest for its potential use in dye-sensitized solar cells, owing to its low viscosity and larger ionic conductivity compared to EMI TFSI. [4,11,21] EMI tris(pentafluoroethyl)trifluorophosphate (FAP), meanwh...

Current options for forming ionic liquid-based solid electrolytes (ionogels) often involve slow processes; however, by leveraging the inherent ability of the ionic liquid to harness the energy of microwave irradiation, a gel-forming, thermal polymerization can be achieved in a matter of seconds. The resulting ionogel electrolyte exhibits comparable electrical and mechanical performance to gels produced via conventional fabrication techniques.